reaper-mcp

An MCP server that lets Claude drive a live, running REAPER DAW instance - transport control, tracks, FX/plugins, MIDI, media items, markers, view/zoom, rendering, and project state - plus a run_reascript escape hatch for anything not covered by a dedicated tool.

Unlike file-parsing REAPER integrations, this talks to REAPER while it's running, and includes an engineer-style discovery layer that finds your REAPER install(s), the running REAPER process (with PID), and whether the bridge is actually reachable - so failures are diagnosable, not silent.

Architecture

Claude  <--stdio-->  reaper-mcp (Python, uv)  <--file-based IPC-->  reaper_bridge.lua (inside REAPER)  -->  reaper.* API

The Python server writes one JSON request file per call into a bridge directory; reaper_bridge.lua picks it up on its next reaper.defer() tick (REAPER's UI frame rate, so ~16-33ms round trips) and writes a JSON response back. No REAPER extensions are required - this uses only the standard io/os Lua libraries and the reaper.* API, both built into vanilla ReaScript. See docs/ARCHITECTURE.md for details.

Related MCP server: REAPER MCP Server

Requirements

• uv (Python package/venv manager)

• REAPER (tested on 6.x/7.x) - nothing else. No extensions to install.

Setup

1. From this repo's root, run:

   build_and_run.bat

   This runs uv sync, copies lua/reaper_bridge.lua into your REAPER Scripts folder, and starts the MCP server over stdio.

2. In REAPER: Actions -> Show action list -> New action -> Load ReaScript..., select reaper_bridge.lua, then Run it. You should see [reaper_mcp] reaper_bridge starting, watching ... in REAPER's console (Extensions -> ReaScript console). Right-click the action and choose "Run on startup" if you want the bridge always live.

3. Point Claude Code (or Claude Desktop) at the server. Example .mcp.json / claude_desktop_config.json entry:

   {
     "mcpServers": {
       "reaper": {
         "command": "uv",
         "args": ["--directory", "<path-to-this-repo>", "run", "reaper-mcp"]
       }
     }
   }

Testing it end to end

1. Open REAPER and load+run reaper_bridge.lua as described above (step 2 in Setup). Confirm the console printed the "watching ..." line.

2. Confirm the bridge is actually reachable, independent of the MCP server, with the CLI diagnostics command:

   uv run reaper-mcp --status

   With REAPER open and the bridge script running, bridge_reachable should be true and running_processes should list REAPER's PID. If it's false, the bridge script either isn't loaded/running in REAPER, or REAPER's resource path doesn't match what was detected - check bridge_dir in the output against the folder the .lua file actually got copied to.

3. Run the batch file if you haven't already:

   build_and_run.bat

   It's stdio-based, so once started it just waits for an MCP client - that's expected, not a hang.

4. Wire it into Claude using the .mcp.json/Claude Desktop config snippet above, then restart Claude Code/Desktop.

5. Exercise it from Claude: ask it to call reaper_status first (sanity check), then something with a visible effect in REAPER, e.g. "add a track named Test" (track_add) or "play" (transport_play), and confirm REAPER actually reacts. track_list is a good read-only check if you want to confirm state without changing anything.

If a tool call errors with "bridge heartbeat not found or stale", the bridge script isn't currently running in REAPER (REAPER was closed, the script was stopped, or it crashed) - reload/rerun it via the Actions list.

Tool overview

Development

uv sync --group dev
uv run pytest

License

Licensed under the MIT License.